In recent years, a cutting tool having a longer tool life than in the case of a conventional cutting tool has been required, along with an increasing demand for highly efficient cutting. Thus, in terms of the characteristics required for tool materials, improvements of wear resistance and fracture resistance, which are related to the life of a cutting tool, have been becoming increasingly important. In view of this, in order to improve such characteristics, a coated cutting tool is widely used which comprises, on a surface of a substrate comprised of a cemented carbide, cermet, cBN or the like, a coating layer consisting of one layer or two or more layers which is/are each comprised of a TiN layer, a TiAlN layer or the like.
Various techniques have been proposed in order to improve the above characteristics of a coating layer. For example, Patent Document 1 proposes a surface coated cutting tool comprising, on a surface of a tool substrate constituted of a tungsten carbide-based cemented carbide, a hard coating layer whose Ti content relative to a total amount of Al and Ti is from 0.15 or more to 0.45 or less (atomic ratio), wherein: the average particle size on a surface of the hard coating layer is from 0.2 μm or more to 0.5 μm or less; the average particle size of a granular crystal grain in the interface between the tool substrate and the hard coating layer is smaller, by from 0.02 μm or more to 0.1 μm or less, than the average particle size of a granular crystal grain on the surface of the hard coating layer; and the proportion of crystal grains, each of which has a particle size of 0.15 μm or less, is 20% or less.